This application claims the priority benefit of Taiwan application serial No. 91134997, filed Dec. 3, 2002.
1. Field of the Invention
The invention relates in general to a thin-film transistor (TFT) liquid crystal display (LCD), and more particularly, to a transflective pixel structure.
2. Related Art of the Invention
The thin-film transistor liquid crystal display is basically constructed with a thin-film transistor array substrate, a color filter array substrate, and a liquid crystal layer. The thin-film transistor array substrate includes a plurality of pixel structures arranged as an array, in which a plurality of thin-film transistors is formed, and each thin-film transistor has a corresponding pixel electrode. Each thin-film transistor has a gate, a channel layer, a drain region and a source region to be used as a switching device of the liquid crystal display.
FIG. 1 shows a top view of a conventional pixel structure, and FIG. 2 shows a schematic cross-sectional view along the line I-Ixe2x80x2 as shown in FIG. 1.
Referring to FIGS. 1 and 2, in the fabrication method of the conventional pixel structure, a gate 102 and a scan line 101 are formed on a substrate 100. The scan line 101 is coupled to the gate 102. A gate dielectric layer 104 is further formed on the substrate 100 to cover the gate 102 and the scan line 101. An amorphous silicon channel layer 106 is formed on the gate dielectric layer 104 over the gate 102, and an Ohmic contact layer 108 is formed on the amorphous silicon channel layer 106. A source/drain region 112a/112b is then formed on the Ohmic contact layer 108. Meanwhile, a data line connected to the source region 112a is defined on the gate dielectric layer 104. The gate 102, the channel layer 106 and the source/drain region 112a/112b construct a thin-film transistor 130. A protection layer 114 is then formed over the substrate 100 to cover the thin-film transistor 130. The protection layer 114 is patterned to form an opening 116 therein. A pixel electrode 118 is formed on the protection layer 114. The pixel electrode 118 is electrically connected to the drain region 112b via the opening 116.
In the above pixel structure, a scan line 101a formed neighboring the pixel structure further comprises a pixel storage capacitor 120. The pixel storage capacitor 120 comprises the scan line 101a (as a bottom electrode), a conductive layer 124 corresponding to the scan line 101a and the pixel electrode (as a top electrode), and the gate dielectric layer 104 formed between the bottom and top electrode. The conductive layer 124 and the pixel electrode 118 are electrically connected via an opening 126 formed in the protection layer 114.
According to the above, the thin-film transistor 130 of the conventional pixel structure is located at a corner of the pixel structure to drive the complete pixel structure, and the pixel storage capacitor 120 is disposed on another scan line 101a. Therefore, the design of such a pixel structure is easy to fail due to process contamination particles. That is, if a contamination particle is attached to a part of the pixel structure to cause defects such as short circuit, the whole pixel structure cannot operate normally. Further, as the pixel storage capacitor 120 is formed on the scan line 101a, an additional stage of design is required for scanning waveform. Therefore, the design and fabrication process of the driving circuit are complex.
In addition, in the conventional transflective liquid crystal display, a plurality of reflective pixel structures and a plurality of transparent pixel structures are used or a semi-transparent film is formed on a substrate to obtain the transflective effect. Currently, a single pixel structure with co-existent transparent and reflective structures to attain transflective effect has not been disclosed yet.
The present invention provides a transflective pixel structure to resolve the problem occurring to the conventional pixel structure.
The present invention further provides a transflective pixel structure with both transparent and reflective structures coexistent in a single pixel structure.
The transflective pixel structure provided by the present invention provides is suitably formed on a substrate. The transflective pixel structure comprises a scan line, a gate dielectric layer, a data line, a protection layer, a transparent pixel electrode, a reflective pixel electrode and a double-drain thin-film transistor. The scan line is formed on the substrate. The gate dielectric layer is formed on the substrate to cover the scan line. The data line is formed on the gate dielectric layer with an extension direction different from that of the scan line. The protection layer is formed on a part of the gate dielectric layer covering the data line. The transparent pixel electrode is formed on the protection layer, and the part of the transparent pixel electrode over the scan line has a plurality of openings to reduce the parasitic capacitance between the scan line and the transparent pixel electrode. The reflective pixel electrode is formed on the exposed gate dielectric layer, with an area equal or unequal to that of the transparent pixel electrode. Further, the double-drain thin-film transistor is formed on the substrate at the center of the pixel structure. The double-drain thin-film transistor has a gate, a channel layer, a source region and two drain regions. The source region is electrically connected to the data line, and the drain regions are electrically connected to the transparent and reflective pixels, respectively. The channel is located on the gate dielectric layer on the gate, the source region and the drain regions are located on the channel layer, and the gate is electrically connected to the scan line.
In the present invention, two edges of the transflective pixel structure further include a first pixel storage capacitor and a second pixel storage capacitor. The first pixel storage capacitor includes a first common line formed on the substrate (as a bottom electrode), a conductive layer over the first common line and the transparent pixel electrode (as a top electrode), and the gate dielectric between the bottom and top electrodes. The conductive layer is electrically connected to the transparent pixel electrode via a contact window formed in the protection layer. The second pixel storage capacitor includes a second common line formed on the substrate (as a bottom electrode), the reflective pixel electrode over the second common line (as a top electrode) and the gate dielectric layer.
As the pixel structure provided by the present invention includes both a transparent pixel electrode and a reflective pixel electrode, the liquid crystal display comprising such a pixel structure has the advantages of transflective liquid crystal display such as power saving characteristic.
Further, as the thin-film transistor is formed at a center of the pixel structure, and two drain regions of the thin-film transistor simultaneously drive the pixel electrodes at two sides, so that the normal operation of the pixel structure can be maintained without being affected by the process particle.
By forming the thin-film transistor on the center of the pixel structure, the electric field on the pixel structure is more uniform and advantageous to display.
As the pixel storage capacitor is not formed on the scan line, the design of the driving circuit of the present invention is simplified.